The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Engines may be operated in a spark ignition (SI) mode and a homogeneous charge compression ignition (HCCI) mode. The HCCI mode involves compressing a mixture of fuel and an oxidizer to a point of auto-ignition. One of the modes may be selected based on engine speed and load. In the HCCI mode, ignition occurs at several locations at a time, which makes a fuel/air mixture burn nearly simultaneously. The HCCI mode performs close to an ideal Otto cycle, provides improved operating efficiency and generates lower emission levels as compared to SI mode. However since there is no direct initiator of combustion, the ignition process tends to be more difficult to control.
The HCCI mode may have various sub-modes depending on the engine speed and load. As the operation changes between the HCCI sub-modes, the engine may misfire due to sudden changes in in-cylinder fresh air due to intake/exhaust valve timing settings and the amount of fuel reforming. Misfires may increase the amount of emissions and reduce the drivability of the engine.